Believed that they once had a cell wall but lost it because of their parasitic relationship with their host.

Compare Gram Positive and Gram Negative Cell Walls

Peptidoglycan Both

Teichoic acids G+

Outer Membrane G-

Lipopolysaccharids (LPS) G-

Porin proteins G-

Periplasm G-

Fluid mosaic model

The mosaic of phospholipids and proteins are not cemented into place but rather they can move laterally in the membrane

Cytoskeleton

Thought it didn't exist until recently

Proteins homologous to those in eukaryotic cytoskeletons are present

Prokaryotes contain a homolog of eukaryotic tubulin.

It forms filaments similar to those found in microtubules. It regulates cell division. Localizes around the neck of the dividing cell where it recruits other proteins needed for the deposition of a new cell wall between the dividing cells.

Proteins homologous to eukaryotic actin

Can help determine cell shape

Crescentin

A homolog to eukaryotic intermediate filaments, also assists in cell shape

Homolog

An entity with similar attributes due to shared ancestry

How many phyla are in the domain Bacteria?

The majority of the 18 phyla of Bacteria play a positive role in nature

Proteobacteria

Contain the largest and most diverse group of species, including E. coli and many human pathogens

Firmucutes

Consist of many gram-positive species, such as Bacillus, Clostridium, Staphylococcus, and Streptococcus

Actinobacteria

Include Streptomyces, the genus that produces the antibiotic streptomycin

Cyanobacteria

Carry out photosynthesis using chlorophyll, responsible for the appearance of oxygen in Earth�s early atmosphere

Chlamydiae

Are extremely small, mostly pathogenic bacteria

Archea

Contain many extremophiles

methanogens (live in anoxic environments)

extreme halophiles (salt-lovers)

thermoacidophiles (grow at high temperatures with low pH)

Crenarchaeota

Tend to grow in hot, acidic environments such as hot springs and volcanic vents

The Archaeal Cell Wall

Provides Mechanical Strength

No archaea have peptidoglycan in the cell wall, but some have pseudopeptidoglycan

Others have polysaccharides, proteins, or both

The S-layer is the most common archaeal cell wall, consisting of protein or glycoprotein in a crystal lattice

The Archaeal Cell Membrane Differs from Bacterial and Eukaryal Membranes

Hydrophobic lipid tails are attached to glycerol differently in archaea

Fatty acids are usually absent

Adjacent lipid tails are bound together forming a lipid monolayer, instead of a bilayer